1. Field of the Invention
The present invention relates to a Public Land Mobile Network (PLMN) selection method and an apparatus thereof. More particularly, the present invention relates to a PLMN selection method for rapidly and efficiently selecting a PLMN when a PLMN selection event occurs in a Roaming state, and an apparatus thereof.
2. Description of the Related Art
When a Public Land Mobile Network (PLMN) selection event occurs in a portable terminal, the portable terminal preferentially selects a registered PLMN (referred to as ‘RPLMN’ hereinafter) stored in a Subscriber Identification Module (SIM) to attempt registration. The RPLMN is a PLMN in which a portable terminal is finally registered. When the RPLMN does not exist or the portable terminal cannot be registered in the RPLMN, the portable terminal selects a Home PLMN (HPLMN) or an Equivalent HPLMN (EHPLMN) to attempt registration. The HPLMN is a PLMN that a user joins, and the EHPLMN is a PLMN that is equivalent to the HPLMN at the time of selecting the PLMN. For example, the EHPLMN can be a PLMN contracting Roaming agreement with the HPLMN.
When the portable terminal is not registered in the HPLMN or the EHPLMN, the portable terminal selects a PLMN by referring to a preferred PLMN list stored in order to have a priority in the SIM by a user or network operator to attempt registration.
For example, when the preferred PLMNs are stored in an order of A-B-C-D, the portable terminal selects a PLMN A according to priority. When the PLMN A is not selected to be greater than a preset Received Signal Strength Indication (RSSI), a PLMN B being second in order is selected. When all the preferred PLMNs are not selected, the portable terminal randomly selects one of scanned PLMNs.
The PLMN selection procedure according to the related art, as described above, preferentially attempts registration in the HPLMN or the EHPLMN when the RPLMN does not exist or the portable terminal is not registered in the RPLMN. However, when a PLMN selection event occurs in a Roaming state, the HPLMN does not exist in a real field. The PLMN selection procedure according to the related art attempts registration in the HPLMN that does not exist in a real field when the PLMN selection event occurs. This increases battery consumption speed and results in unnecessary time consumption at the time of selecting the PLMN. Upon selecting the PLMN, the PLMN selection procedure according to the related art randomly selects one PLMN when priority does not exist or when the PLMNs have the same priority, to attempt registration. When the registration is not achieved, the PLMN selection procedure according to the related art selects another PLMN to attempt the registration. The PLMN selection procedure attempts the registration by selecting the PLMN one by one which results in unnecessary time consumption and battery consumption speed.